1. Technical Field
The present invention relates to a method and apparatus for rapidly changing constituent components and reducing change over waste in the extrusion process of manufacturing synthetic fiber. More particularly, the present invention relates to an improved system for proportioning, mixing and distributing components, such as color pigments, with a base polymer to selectively deliver flow streams of a wide range of colors or other characteristics to spinneret extrusion holes.
2. Discussion of the Prior Art
Synthetic fibers are produced by pumping fluid polymer through an assembly called a spin pack consisting of a series of component plates that collectively filter, distribute and finally extrude the fibers through fine holes into a collection area. Multi-component fibers (i.e., fibers consisting of more than one type of polymer) are extruded from spin packs having one or more distribution plates having slots, channels and capillaries arranged to deliver the polymer from one, or a few, inlets to the hundreds of extrusion holes. Exemplary of such spin pack assemblies are those disclosed in U.S. Pat. No. 5,162,074 (Hills) consisting of, in order, an upstream top or inlet plate, a filter screen support plate, a metering plate that communicates filtered melt to an etched distribution plate that in turn disperses the melt laterally to multiple extrusion through-holes formed in a final downstream spinneret plate.
The addition of coloring pigments or dyes to the polymer melt has been generally performed outside and upstream of the spin pack with the cost-inefficient result that the entire pack has to be cleaned or flushed between each change in fiber color. Representative of this longstanding approach is U.S. Pat. No. 2,070,194 (Bartunek, et al) disclosing a system characterized by premixing separate batches of cellulosic solutions with a plurality of primary colors, pumping selected proportions of the various colored solutions into a common mixing tank to produce a desired fiber color, and then pumping the mixed solution to a filament forming machine.
An alternative approach, exemplified by U.S. Pat. No. 5,234,650 (Hagen et al) pumps three or more streams of differently colored premixed polymer to a program plate directly upstream of the spinneret. The program plate blocks, meters or permits free flow of each of the streams into the active backholes. Color or component combinations are controlled by flows permitted to reach each backhole, but the program plate must be replaced to change the characteristics of the fiber or yarns produced and this creates delays and expense. Moreover, no effort is made to actively mix the color combinations beyond the merging of flows.
The delivery of metered amounts of separated polymeric components to spinneret nozzles to extrude combined multi-component fibers, particularly trilobal fibers having abutting sheaths and cores of different characteristics, is illustrated by U.S. Pat. No. 5,244,614 (Hagen) but again no teaching of the utility of, or procedure for, homogeneously mixing the separate components is provided. Instead the molten polymer is merged into a single capillary communicating directly with the extruding orifice.
The known prior art nowhere presents a technique nor an apparatus for selectively combining and mixing constituent fiber components, such as pigments or precolored polymer streams, immediately upstream of the spinneret in a continuous flow process. Such a procedure would reduce processing interruptions, expenses and waste by minimizing the residence time and consequently the constituent material required to effect a transition from a fiber of one selected characteristic to another.